Cord Placement Model: An Instructional Guide for Preclinical Dental Students to Practice the Skill of Retraction Cord Placement

Introduction Gingival displacement is essential for ideal margin exposure and improved direct or indirect restorative outcome. Recent literature found many dentists prefer using retraction cord. Some contraindications of other displacement methods make retraction cord displacement preferred. It is necessary to teach dental students appropriate cord placement while minimizing gingival trauma. Methods We developed a stone model using prepared typodont teeth and simulated gingiva that was made of polyvinylsiloxane material. Twenty-three faculty and 143 D2 students were briefed on the instructional guide. After faculty demonstration, D2 students practiced for 10–15 minutes under observation. The following year, former D2 (now D3) and D4 students were asked for feedback on the instructional experience. Results Fifty-six percent of faculty rated the model and instructional guide good to excellent, and 65% rated the student experience as good to excellent, with only one participant rating it poor. Seventy-eight percent of D3 students strongly agreed or agreed the exercise increased their understanding of the technique in placing cord on a patient. Furthermore, 94% of D4 students strongly agreed or agreed having this exercise in preclinical D2 year would have been helpful. Discussion Use of retraction cord to deflect gingiva is still preferred by most dentists. Completing the cord placement exercise on a model helps prepare students to perform the procedure on a patient before arriving at the clinic. Survey comments such as “useful exercise” support use of this instructional model. Overall, faculty and D3 and D4 students felt the exercise was beneficial to use in preclinical education.


Introduction
Gingival displacement (GD), sometimes referred to as retraction, is defined as deflection of the gingival margin away from the tooth. 1 Displacing the gingiva creates adequate vertical and lateral space between the preparation finish line and gingiva to allow the injection of sufficient bulk of impression material into the sulcular space. Also, it can enhance the scanning of gingival margins. Accuracy of an impression and marginal fit of the restoration depend on several aspects, one of those being adequate GD. Gingival retraction is sometimes advantageous when placing direct restorations. Substandard adaptation of restorations with subgingival margins can cause the accumulation of plaque biofilm, leading to gingival inflammation and caries. 2 Gingival retraction can be achieved by mechanical, chemical, or surgical (electrosurgery or laser) methods. However, laser is contraindicated in the presence of nitrous oxide or where there is a lack of attached gingiva. Retraction cord is the preferred option for GD. It is considered the most common method for gingival management. 3 A 2008 study found that 92% of dentists used displacement cord, 20% used a soft tissue laser, and 32% used electrosurgery. 4 Another indication for GD with retraction cord is in the cementation of a restoration. The tooth is isolated to help control moisture from gingival crevicular fluid. 5 This also helps to contain the amount of cement pushed into the sulcus. A more recent survey of dentists found the majority continues to use retraction cord for GD due to predictability. 6 Dental operators who choose cord for retraction must develop safe and effective methods for placement. If the cord is inappropriately manipulated, it can lead to trauma and recession from excessive pressure and the amount of time it is left in the sulcus. 1,4 It is therefore essential for dental programs to teach students the criteria for the gingival retraction technique. Furthermore, when cord is the selected technique, students need to develop the proper approach to cord placement to minimize injury to the gingiva and maintain periodontal health of their patients. Typodonts provided for skills training on simulation manikins traditionally do not have a sulcus for practicing retraction cord placement. Additionally, literature on procedural techniques is lacking, and there are no similar MedEdPORTAL publications. Therefore, we identified the need to create a stone model with a sulcus for students to practice retraction cord placement on before providing direct patient care.

Cord Packing Model Fabrication
We fabricated a stone model with two to six plastic teeth prepared for full crown restorations, as described in the Retraction Cord Model Fabrication Instructional Guide video (Appendix A). Gingival tissue was simulated using medium body polyvinylsiloxane impression material. To maintain costeffectiveness, teeth that had previously been prepared by students for full crowns were used to fabricate the models. We tested the models with a focus group of five clinical faculty members to preassess them as a teaching tool and aid in developing a postexercise survey. A printed version of the stepby-step Instructional Guide for Fabricating a Retraction Cord Packing Model (Appendix B) was available as an adjunct to the video.
Faculty Perception of Cord Placement Activity Prior to this simulation activity, we met with the faculty who would be leading the student exercise. Verbal informed consent that described the purpose of their participation in a survey to assess the cord packing activity was given (Institutional Review Board AZ# 1429). We reviewed the students' instructional guide (Appendix C) with faculty as well as the overall goals for the session. To measure the effectiveness of the activity, we distributed a survey (Appendix D) to the faculty to gather their perceptions of the instructional guide and cord packing model as an educational tool.

Implementation
To teach the exercise, we created the cord packing model fabrication video (Appendix A) along with the step-by-step instructional guide (Appendix B). The target audience for this activity was second-year preclinical dental students; the activity itself was an exercise in the simulation laboratory, course number 1636L. The students were just beginning the spring session and preparing for transition to clinic. They had previously received 2 hours of classroom presentations describing measures to facilitate tissue management and fluid control during impression procedures. The video reviewed tissue retraction techniques, when they should be used, and how those results would lead to an acceptable impression.
We created a 20-slide PowerPoint (Appendix E) to use at the commencement of the activity for review. The first portion of the presentation provided background information regarding the use of lasers, cord, and electrosurgery for GD. The second half reviewed cord placement technique. Faculty could determine the appropriate use of the PowerPoint presentation based on student need. We also created a short video of the students' instructional guide (Appendix F) for faculty and/or student reference as needed. The implementation guide (Appendix G) provided overall guidance in facilitating the simulation exercise.
We asked instructors to distribute the instructional guide to the students and verbally review the goals for the exercise. The faculty-to-student ratio was 1:5. Instructors demonstrated the retraction cord placement technique to small groups. Following the demonstration, students received one-on-one opportunities to practice the technique for 10-15 minutes with verbal feedback from faculty. As this session was included as part of a larger daily simulation activity, no formal assessment was provided. The session was a completion exercise supported by verbal faculty feedback. We developed the cord packing assessment (Appendix H) to evaluate students' skill at completion of the exercise.
To gain further understanding of the students' experience, we expanded the activity to a convenience sample of third-and fourth-year students (n = 71) the following year. Verbal informed consent that described the purpose of participation was given by the students. The groups surveyed were D3s (formerly D2s) and D4s who had not previously experienced the exercise. The D4s (n = 34) were 3 months from completion of their clinical education. A survey for D3s (Appendix I) and a separate survey for D4s (Appendix J) were used to assess their perception of the exercise. This student cohort had the opportunity to review the instructional guide and practice on the cord placement technique model. The goal of involving the D4 students was to retrospectively determine if they felt it would have been helpful to have had the exercise during their preclinical education.

Results
Faculty Perception of the Cord Packing Exercise Twenty-three faculty completed the survey following the simulation exercise for cord placement ( Table 1). The majority of faculty completing the survey (78%) agreed the model was representative of the experience of placing retraction cord on a patient. Conversely, 21% disagreed or strongly disagreed ( Table 1). The overall rating of the model and instructional guide provided a range of responses from poor to excellent. The majority (56%) rated them good to excellent, while 43% rated them fair. The faculty perception of the overall student experience rated more positively, with 65% rating it good to excellent. Thirty percent of faculty gave a fair rating, and only one survey participant rated the experience as poor (Table 1).

Students' Perception of the Cord Packing Exercise
The exercise was first presented to a D2 class of 143 students. There was no formal assessment, so the actual number of participants could not be identified. Some of the students who had completed the cord placement exercise in the D2 year were surveyed in their third year (n = 37) of clinic (Table 2). We surveyed these students 9 months after their full-time transition into clinic. Forty-nine percent of these participants strongly agreed or agreed that the training model in the D2 year prepared them for placing cord on patients, while 17% had no opinion. Twenty-six percent of the students disagreed (Table 2). Of the D4 students (n = 34, Table 3), 94% strongly agreed or agreed that having the exercise in preclinical D2 year would have been helpful. One of the 34 participants had no opinion of the exercise, while one participant disagreed that it was helpful (Table 3).
We read the open-ended survey comments of D4 students and faculty to identify recurring themes (Table 4). Most comments were related to the retraction cord packing model design. The second most prominent theme centered around the model activity as a learning resource. Comments regarding the instrument used for the exercise came only from the faculty. There were several comments from students regarding performing cord placement in vivo.

Discussion
Gingival retraction cord is used to provide the dentist with a clear working view of a tooth and its prepared margins prior to taking the impression. This can be captured with impression material or scanned digitally. In one study, although in vitro, Son and Lee 7 discovered a 63% improved accuracy of intraoral scans of subgingival margins with the use of GD cord. Becoming competent in retraction cord placement is an essential skill for enhancing restoration success even in the case of digital dentistry. Gottlieb, Vervoorn, and Buchanan 8 suggested that an acceptable level of competence should be obtained prior to clinical patient care because most dental procedures are irreversible and learning them solely on patients is not a suitable practice. In our survey, 74% of D4 student participants strongly agreed or agreed that the model was representative of the experience of placing retraction cord on a patient. However, approximately one-fourth (26%) of D3 students disagreed that the model prepared them for placing cord on a patient. There could be several reasons for this response. The activity that day was one of several exercises of the daily session and was not assessed upon completion; hence, there was no record of which students completed the exercise. Some students mentioned that they were not present that day and therefore did not have the chance to practice in their D2 year simulation lab.
Traditionally, our students learn how to pack retraction cord from on-the-job training when they arrive at the clinic. While our exercise activity is not an exact replication of cord placement on a patient, it allows students to gain knowledge of a set of skills that  they would otherwise learn only on their first patient encounters. This set of skills includes the proper instruments to use, as well as appropriate technique to pack the cord with minimal trauma to the gingiva. Comments from faculty such as "not realistic but good exercise" and "doesn't simulate same feeling of placing cord but still useful exercise" support the use of this instructional model. Furthermore, dental student comments such as "good but doesn't mimic gingiva, good starter," and "closest representation of what it is like to place cord" are further support of the need for using the cord placement model for training.
Dental students were also given the opportunity to experience using more than one type of cord placement instrument. One repeated comment from faculty survey participants related to the serrated cord placement instrument used for the exercise. It was described as "poor" and was said to have easily "pulled [the] cord out"; one commenter "rec[ommended] non serrated cord packer." Interestingly, the D3 and D4 students commented that they liked using the serrated cord placement instrument better than the plain Teflon-coated one available in the clinic. Because of their comments, we are considering offering more than one type of cord placement instrument in the future.
Based on participant responses regarding the instructional model, we modified the fabrication technique before presenting the exercise to the third-and fourth-year students. Due to faculty comments such as "[did] gingivectomy to make sulcus, then worked well," and "need sulcus, difficult to pack cord," we created a sulcus on the model before presenting to the D3 and D4 students. Those modifications are reflected in the model fabrication video and step-by-step guide (Appendices A and B). Faculty members from the original focus group that assessed the model evaluated the revised model and felt the revision of the simulated sulcus was a better representation of the clinical experience.
A limitation of the evaluation approach in our exercise was the use of two different iterations of the model design. Faculty feedback gathered was based on the initial model design without the sulcus. The same models were used with the D2 students who participated in the first activity. After we modified the model design with a sulcus, feedback from the D3 (former D2) and D4 students was positive, although several students commented that one big challenge of cord placement was having to use indirect vision. The inability to mount the model into a manikin is another limitation to the cord packing exercise. We will consider taking on the challenge of developing a technique for mounting the model.
Broader implications for including this activity in preclinical simulation are the skill and practice required to place retraction cord. Improper cord placement can cause gingival injury and damage to the sulcular epithelium. This can lead to recession